The interaction of macrophages with an obligate intracellular microbe (Toxoplasma gondii) and a facultative intracellular microbe (Mycobacterium tuberculosis) will be studied. The intracellular events associated with phagocytosis of these microbes by macrophages from normal and immunized animals will be studied using phase contrast and electron microscopy, radioactive labelling techniques, and C14-1-glucose utilization and calculation of generation times. The effect of sensitized lymphocytes and lymphokines on the intracellular events in macrophages after phagocytosis of toxoplasmas or mycobacteria will also be investigated. The lymphokine will be characterized, the role of specific antigen determined, and the requirements for a metabolically active macrophage determined. It is expected that study of this lymphocyte macrophage model will add important dimension to our knowledge of intracellular parasitism and cellular immune responses.